Multi-stage rotary vacuum pump with separate oil reservoir

ABSTRACT

An improved vacuum pump of the rotary mechanical type having interchangeable component parts which may be assembled in &#39;&#39;&#39;&#39;building block&#39;&#39;&#39;&#39; fashion to provide single and multi-stage pumps built up from the same basic parts. The multi-stage pump may be provided with a switchable feature whereby the stages may be operated in series or in parallel, with automatic switching therebetween if desired. Both air ballast and oil injection are provided, the latter incorporating a check valve to control the supply of oil to the pumping chamber.

ilited States Patent Fritch et al.

[ 1 Sept. 24, 1974 MULTl-STAGE ROTARY VACUUM PUMP WITH SEPARATE OIL RESERVOIR [75] Inventors: Junior L. Fritch, Edgerton; Don R.

Brandeberry, Montpelier, both of Ohio [73] Assignee: Robinair Manufacturing Corporation, Montpelier, Ohio [22] Filed: Nov. 12, 1973 [211 App]. No.: 414,695

Related US. Application Data [63] Continuation of Ser. No. 252,213, May 11, 1972,

Pat. No. 3,791,780.

[52] US. Cl 417/62, 418/11 [51] Int. CL... F04b 23/04, FOlc 11/00, F040 23/00 p [58] Field of Search 417/62; 418/5, 9-13, 418/60, 67, 97-99, 210, 212, 213

[56] References Cited UNITED STATES PATENTS 1,719,747 7/1929 Bandoly 418/212 2,063,503 l2/l936 Hermsdorf et al 418/60 2,208,273 7/1940 Karasick 418/5 2,492,075 l2/l949 Van Atta 417/62 3,107,047 10/1963 Lorenz 418/97 Primary ExaminerC. J. Husar Assistant Examiner-John J. Vrablik Attorney, Agent, or FirmBurton and Parker [5 7] ABSTRACT An improved vacuum pump of the rotary mechanical type having interchangeable component parts which may be assembled in building block fashion to provide single and multi-stage pumps built up from the same basic parts. The multi-stage pump may be provided with a switchable feature whereby the stages may be operated in series or in parallel, with automatic switching therebetween if desired. Both air ballast and oil injection are provided, the latter incorporating a check valve to control the supply of oil to the pumping chamber.

3 Claims, 13 Drawing Figures PATENTEDSEPEMSH war-w 1 PAIENIEDsEmwn SIEUGB! 7 w m. 4 ra 9 1/4 0! IGJ? MULTI-STAGE ROTARY VACUUM PUMP WITH SEPARATE OIL RESERVOIR This is a division of application Ser. No. 252,213 filed May 11, 1972 now US. Pat. No. 3,791,780.

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to vacuum pumps, and more particularly to an improved rotary mechanical vacuum pump.

2. Description of the Prior Art Rotary mechanical vacuum pumps of the vane type, in which an eccentric cylinder or a rotor rotates within a hollow cylindrical chamber with a reciprocating vane extending through the chamber wall and journalled in the periphery of the rotor to provide separation between the inlet and outlet ports have long been known, as exemplified by US. Pat. Nos. 1,530,973; 2,929,550, and others. Both single and multi-stage pumps of this general type are known, and the prior art shows many specific features of construction, such as for example the oil injection feature of US. Pat. No. 2,929,550 and the multi-stage pump of US. Pat. No. 3,525,578 utilizing a single hollow rotor to effect stage-to-stage gas conductance.

A salient feature of the vacuum pump construction disclosed herein is that pumps of various capacities, including both single and multi-stage pumps, may be constructed utilizing the same basic components. The pumping section of the vacuum pump disclosed comprises a plurality of block-like members which are stacked in face-to-face relation, and various numbers of these members may be stacked in building block fashion to provide either single or multi-stage pumps. The oil reservoir section of the vacuum pumps disclosed is a completely separate member which is mounted atop the building blocks of the pumping section, facilitating manufacture and appreciably reducing manufacturing cost. Surmounting the oil reservoir section is a cover or top cap section which in the case of the multi-stage pumps may be provided with suitable manifold passages and valving to permit the pump stages to be operated either in series or in parallel. Thus, a multi-stage vacuum pump having identical pumping section and reservoir section parts may be converted from a series operated pump to a seriesparallel operated pump merely by replacing the top cap section with a modified section of the same general structure and dimensions.

Another feature of the vacuum pump disclosed herein is the novel oil injection structure wherein the oil injection passage extends from the bottom of an oil sealing ring groove between the building blocks of the pumping section upwardly into the pumping chamber, the oil passage being controlled by a check valve means. By taking the injection oil from the lowermost portion of the oil groove, which communicates at its upper end with the oil reservoir, the oil within the pump is constantly being circulated throughout the pump. In addition, the contaminants in the pump oil, which are usually heavier than the oil, will gravitate to the bottom of the oil groove, and will be injected with the oil into the pumping chamber. As the condensed contaminants are injected into the chamber at low pressure, they will be vaporized and exhausted through the pump outlet as a gas, thereby purging the pump oil of entrained contaminants.

Another advantageous feature of the particular oil injection mode employed arises from the provision of the check valve in the oil injection passageway, which valve may be adjusted to admit the ideal amount of oil into the chamber during each pump cycle. Furthermore, the provision of the oil injection valve substantially eliminates the hydraulic hammer which is prevalent in the prior art designs which relied on the rotating piston to close the oil orifice into the chamber. With these prior art designs, the oil would be forced back up through the oil injection passageway into the reservoir, and would bubble up through the oil in the reservoir, creating an audible hydraulic hammer.

SUMMARY OF THE INVENTION A vacuum pump of the rotary piston type having a generally radial vane extending from the piston periphery through the side wall of the pumping chamber, a separate oil reservoir mounted atop the pumping chamber, and a cover surmounting the oil reservoir, with oil injection means comprising an oil conducting passage leading from the bottom of an oil groove upwardly into the pumping chamber through a side wall thereof, said passage having adjustable check valve means therein to control the supply of oil into the chamber and prevent oil flow through the passage in the reverse direction.

The pumping section of the vacuum pump embodying the invention comprises a plurality of members stacked in face-abutting relation, at least some of which members are provided with oil grooves extending in spaced circumferential relation about the pumping chamber to provide an oil seal between the members. These oil sealing grooves communicate at their upper ends with the oil reservoir and at their lower ends with each other, and with the oil injection passage. There are in addition oil sealing grooves provided between the pumping section members and the oil reservoir member to effect a fluid-tight seal therebetween. This eliminates the need for any mechanical type seals between the various parts of the structure. In the multistage pump, a novel manifold cover member or top cap surmounts the oil reservoir section, which may be provided with suitable valves so that the pump may be either manually or automatically switched between parallel and series operation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a double stage mechanical vacuum pump embodying the invention, the pump being directly driven by a suitable electric motor;

FIG. 2 is an exploded perspective view of the pump shown in FIG. 1 illustrating the relationship of the lower pumping section, the intermediate oil reservoir section, and the upper top cap section;

FIG. 3 is a vertical section taken along line 3-3 of FIGS. 1 and 2;

FIG. 4 is a vertical section taken along line 4-4-of FIGS. 1 and 2;

FIG. 5 is an exploded perspective of the pumping section of the vacuum pump showing the building block feature and the relationship of the various internal parts;

FIG. 6 is a partial cross-section taken through the lower portion of one of the building block end plates,

generally along the line 6-6 of FIG. 12, illustrating the oil injection passage with the check valve disposed therein;

FIG. 7 is a top view, partly in section, through the top cap of the pump, taken along line 7-7 of FIG. 2;

FIG. 8 is a partial section taken along line 88 of FIG. 3 showing details of the chamber outlet stack;

FIG. 9 is a bottom elevation of the oil reservoir section taken in the direction of the arrow 9 in FIG. 2;

FIG. 10 is a cross section through the pumping section taken along line 10-10 of FIG. 4;

FIG. 11 is a partial section taken along line 11--l1 of FIG. 10 showing details of the manually operated oil drain valve;

FIG. 12 is a partial section taken along line l2--12 of FIG. 6 showing further details of the oil injection feature; and

FIG. 13 is a schematic representation of means for automatically switching the two pump stages between series and parallel operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, and more particularly initially to FIG. 1, there is shown therein a vacuum pump of the rotary mechanical type comprising in general a lower pumping section 22, and intermediate oil reservoir section 24 and a top cap or manifold section 26. The pump 20 is connected in direct drive relationship to a conventional electric motor 28, but it will be obvious to those skilled in the art that the pump could be driven in other manners, as for example by a belt drive, in which event the pump shaft and motor shaft could each be provided with suitable pulleys, with a drive belt entrained about the pulleys in well known fashion.

The pumping section 22 of the pump 20 comprises a plurality of members 30, 32, 34, 36 and 38 shown most clearly in FIGS. 2 and 5, which members are of identical exterior configuration and of generally rectangular cross section, the members being secured together in surface abutting relation or stacked together as shown in FIG. 2 and secured by through bolts or the like 40. The end-most members or building blocks 30 and 38 constitute end plates which serve as closure members for the pumping chambers defined by the members 32 and 36, with an intermediate closure member 34 being interposed between the members 32 and 36 as shown.

Each of the closure members 30, 34 and 38 are provided with oil sealing grooves 42, the members 30 and 38 having such a groove in only one end face thereof, while the member 34 has a groove in both end faces thereof. The oil sealing grooves 42 in all of the members are substantially identical, and each comprises a generally circular portion 44 and a pair of upwardly extending portions 46 and 48 opening through the top face of the respective member. The mating faces of each of the building blocks 30, 32, 34, 36 and 38 are finished by a grinding or milling operation to be completely flat and smooth and are preferably coated with suitable grease or the like before assembly, and then the members are securely mounted in surface-abutting relation and secured by the through bolt 40 shown in FIG. 2.

The pumping chamber blocks or units 32 and 36 are basically identical, and a description of the member 32 will suffice for both. Member 32 is provided with a cylindrical aperture 46 extending therethrough which defines a pumping chamber within which is positioned a cylindrical rotor or displacer 48 having a generally radially extending vane attached thereto and projecting through a slot 52 beyond the upper face of the block. By reference to FIG. 3 it can be seen that the vane 50 is provided with an enlarged cylindrical lower end 54 interfitting in a correspondingly shaped recess or socket in the rotor 48, and the rotor or displacer is in turn mounted eccentrically on a drive shaft 56 which extends completely through both pumping chambers and beyond the end wall of member 38 for connection to the drive motor 28. The rotor 48 is driven in conventional fashion, and as the rotor rotates, the vane is reciprocated within its slot 52, serving as a separating wall between the pump chamber inlet and outlet, as will be described more fully hereinafter. Each of the oil sealing ring grooves 42 in the various members 30, 34

and 38 extends in circumferentially spaced relationship around the pumping chambers 46 of members 32 and 36 and as the grooves are completely filled with oil from the oil reservoir section 24 to be described, the grooves 42 provide an effective oil seal for the pumping chambers.

In FIG. 3 the pumping member 32 is shown in section, and includes an inlet 58 and outlet 60 opening into the chamber 46 on opposite sides of the vane 50 and spaced closely adjacent thereto. The outlet 60 is provided with a check valve comprising a ball 62 surmounted by a spring 64 to prevent reverse gas flow back into the chamber 46 and in addition exhibits a laterally offset passage portion 66. Referring to FIG. 4, pumping member 36 is provided with identical parts, which have been labelled with corresponding numbers primed to distinguish them from parts of the member 32.

Mounted atop the offset outlet passage portion 66 is a stack or chimney 68 comprising a vertically opening bore or passage 70 establishing communication between the passage 66 and the oil reservoir at a point spaced above the oil level therein and a laterally offset counterbore portion 72 which serves as a seat for the valve spring 64. The stack 68 may be secured to the top face of the member 32 as by screws or the like which are shown in cross section at 74 in FIG. 8. An identical stack 68 is disposed atop the outlet of chamber 46 as shown in FIG. 4. By providing the offset passage portions 66 and 66, the gases out of the respective pumping chambers 46 and 46' may pass unrestricted to the stack bores 70 and 70 as soon as the associated ball is lifted from its seat, as the gases do not have to pass around the ball, but flow laterally thereof through these offset passages.

The intermediate oil reservoir section 24 is a onepiece member, preferably being of cast metal or the like which member surmounts the building block members of the pumping section 22 and is secured thereto as by cap screws or the like, two of which are shown at 76 in FIGS. 3 and 4. The reservoir section 24 is divided by interior wall means 78 to define two separate oil reservoirs 80 and 82 the former of which communicates with the pumping chamber 46 defined by the member 32 (FIG. 3) while the latter communicates with the pumping chamber 46' defined by the member 36 as shown in FIG. 4. Referring to FIG. 3, the member 24 is provided with a generally vertical inlet passage 84 having a laterally offset lower end portion 86 communicating with the pumping chamber inlet 58 and an outlet passage portion 88 which communicates with the pumping chamber outlet 60 through passage 66, stack bore 70 and reservoir 80. Similarly, as shown in FIG. 4, the reservoir section 24 has an inlet passage 90 extending generally vertically therethrough and having a laterally offset portion 92 communicating with inlet 58 of pumping chamber 46 and an outlet 94 through section 26 to be described, which communicates with chamber outlet 60 through the passage 66, stack bore 70 and the oil reservoir 82.

A gas baffle 96 is disposed within the reservoir 82, and is secured to a portion of the oil reservoir section 24 as by cap screws or the like 98 (FIGS. 3 and 4). Baffle 96 is preferably constructed of a non-corrosive sheet metal or the like and comprises a base portion 100 and a leg portion 102, the base portion being of substantially W-shape and the leg portion being of inverted V-shape, as shown most clearly in FIG. 2.

Referring now to FIG. 9, which is a view of the lower face of the oil reservoir section 24, the oil reservoirs 80 and 82 are shown in plan view. Also shown are the inlets 84, 86 and 90, 92 previously described. Surrounding the inlet 84, 86 is a shallow groove cut in the lower surface 104 of the oil reservoir section 24, such groove defining a continuous cutout having portions 106 and 108 extending on opposite sides of the inlet 84, 86, and portions 110 and 112 extending in spaced parallel relation on opposite sides of the reservoir 80 and outlet 88, which portions communicate at their ends 114 and 116 respectively with oil reservoir 82. The above mentioned groove portions are innerconnected by an end groove portion 118 and by an intermediate crossover groove portion 120, all of the groove portions being in communication with each other and thus with the oil reservoir 82.

As can be seen from FIG. 3, the groove portions 118 and 120 extend in spaced relation at opposite ends of the inlet 86, and as the grooves all communicate at the extremities 114 and 116 with the oil reservoir 82, when oil is introduced into such chamber, it flows into the grooves, filling them with oil, and effectively sealing the innerface between the oil reservoir section 24 and the members forming the pumping section 22. Likewise, a generally U-shaped groove 122 is formed in the surface 104 of member 24 extending in spaced relation around the inlet 90, 92 of the remaining pump stage, and has opposite end portions 124, 126 communicating with the oil reservoir 82 to provide an effective oil seal about the inlet 90, 92. The grooves 118 and 120 are shown in cross section in FIG. 3, while the bight portion of the oil groove 122 is shown in cross section in FIG. 4.

As can be seen from FIG. 2, the oil reservoir section 24 may be provided with a series of counterbored vertical apertures 128 extending generally vertically therethrough, and the members forming the pumping section 22 may be provided with aligned threaded apertures 130, and the sections 24 and 22 may then be secured together by cap screws or the like, one of which is shown at 132 in FIG. 2, in addition to the screws 76 previously described.

Mounted atop the reservoir section 24 is a top cap or cover section 26 which is shown in FIGS. 1, 2, 3, 4 and 7. The top cap section 26 may be conveniently secured to the oil reservoir section 24 as by a series of cap screws or the like 134, some of which are shown in FIGS. 2, 3 and 4, and if desired a suitable gasket (not shown) may be interposed between the mating surfaces of the sections 24 and 26. The top cap 26 includes a cover plate portion 136 and a manifold portion 138, the latter being disposed directly above the pumping chamber 46 as shown in FIG. 3. A longitudinally extending valve chamber 140 opens through one end of the manifold 138 and has disposed therein a spool valve 142 having spool portions 144 and 146 encircled by suitable seals 148. The valve 142 may be fitted for manual actuation by being provided with a handle 150 having a knob 152 on the outer end thereof, the handle projecting out of the manifold section 138 through an L-shaped slot 154 (FIG. 2).

Adjacent one end of the manifold portion 138 is an inlet passage 156 having an internally threaded open end 158 adapted to be coupled to the device to be evacuated, the lower end of the inlet 156 communicating with the inlet passage 84, 86 in section 24 and thence with the pumping chamber 46 through the passage 58 as shown in FIG. 3. An outlet passage 160 establishes communication between the outlet 88 from the pumping chamber 46 and the valve chamber 140. An additional passage 162 establishes communication between the valve chamber 140 and the reservoir 82, and the passages 160 and 162 are in communication with the spool valve 142 in the position shown in solid outline in FIG. 3. The valve chamber 140 in addition communicates with another passage 164 in top cap 26, the passage 164 having a laterally extending portion 166 (FIG. 7) formed by a cutout in the underside of the member 26, and communicating at its opposite end with the inlet 90, 92 through passage portion 168 (FIGS. 7 and 4). The outlet 94 from the reservoir 82 previously described is provided with internal threads, and a muffler 170 having an externally threaded fitting 172 is threadably engaged in the aperture 94.

Means for introducing ballast air into the pumping chamber 46' is shown in FIG. 10, such means comprising an air passage 174 opening laterally into the chamber from the block member 38, with the outer end of the passage 174 having a fitting 176 threadably engaged therewith communicating with an upstanding tube 178 defining an internal air passage 180 and a lateral passage 182 opening to atmosphere. The upper end of the tube 178 is suitably designed to accept a needle valve 184 having a valve body portion 186 adapted to seat against a nylon insert in the port establishing communication between passages 180 and 182 as shown in FIG. 10. Valve 184 is provided with a knob 188 so that the valve body may be manipulated to open and close the port. Valve 184 is not intended as a metering valve, the passage 174 being of a predetermined diameter to admit only the necessary air to the pumping chamber 46' for ballast purposes when the valve is open, the rotating pistons 48' closing off the inner end of the aperture 174 as the piston rotates in the exhaust stroke, as more fully described hereinafter. The position of the passage 174 at its opening into the chamber 46 is shown in dotted outline in FIG. 4.

Shown in FIGS. 6 and 12 most particularly is the structure for the oil injection into the pumping chamber 46', and referring first to FIG. 6, a vertical aperture 190 is formed in the block member 38, and the lower end of the aperture is then plugged by a threaded plug 192. The vertically extending passage 190 communicates with the oil groove 42 at the lower portion thereof through short aperture 193, and continues upwardly into communication with a small laterally disposed aperture 194 which establishes communication'between the passage I90 and the pumping chamber 46. The relative position of the oil injection aperture .194 with respect to the end wall of the pumping chamber 46' is indicated in dotted outline in FIG. 4. Disposed within the vertical passage 190 above its point of communication with the oil groove 42 is a sleeve member 196 having a passage 198 opening therethrough, the sleeve being surmounted by a valve body 200 which is biased by a spring 202 against the sleeve 196. The valve body 200 may be T-shaped in cross section, having a cylindrical head seated against the sleeve 196 and a cylindrical body portion of lesser diameter projecting upwardly from the head and over which the spring 202 is received bearing against the head and biasing the valve body against the upper end of the sleeve 196, thereby closing the passage 198.

Spaced a short distance from the passage 190 is a laterally extending aperture 206 as shown in FIGS. 6, l and 11, communicating at its inner end with the bottom of the oil groove 42. At its outer end, the aperture 206 has a shut-off valve assembly 210 threaded thereinto, the valve 210 having an outlet 212 open to the atmosphere. The block members 32, 34 and 36 are provided with lateral openings 214, 216 and 218 respectively which are in axial alignment with and communicate with the aperture 206 and with all of the oil grooves 42. Therefore, the provision of the manually operable valve 210 permits the entire oil supply in the vacuum pump to be drained easily and conveniently.

Referring to FIGS. 3, 4 and 10, it can be seen that the shaft 56 is journalled in the member 38, and extends completely through the members 36, 34, 32 and 30 and outwardly therebeyond for connection to the drive motor 28 (FIG. 1). A suitable seal 220 is provided in the member 30 surrounding the shaft 56, and the shaft 56 extends axially through the pumping chambers 46 and 46. The rotors 48 and 48 are eccentrically mounted on the shaft 56 in opposed positions of eccentricity, as shown in FIGS. 3 and 4. Each of the end blocks 30 and 38 is provided with a generally vertically extending aperture 222 and 224, which apertures communicate with the oil reservoir at their upper ends and and with the shaft 56 at their lower ends to lubricate the shaft.

As shown in FIGS. 2, 3 and 4, each inlet to the pumping chambers is provided with a ball 226 and 228 respectively made of a non-corrosive, comparatively lightweight material such as hollow aluminum. The balls are positioned to rise into contact with the seat portions 230 and 232 respectively of the inlets to prevent oil flow from the respective pumping chambers back through the inlets. If the pump is stopped while connected to a device being evacuated, and the device is under vacuum, the oil in the pump will tend to be sucked into the device. The halls 226 and 228 prevent this from occurring.

An aperture 234 is provided in the end wall of the oil reservoir section 24, and a transparent window member 236 is disposed therein, for visual inspection of the oil level within the oil reservoir. The oil level in the oil reservoirs 80 and 82 is preferably maintained slightly below the top of the stacks 68 and 68, so that the gas issuing from the pumping chamber outlets is exhausted through the stacks above the level of oil in the reservoir and impinges against the baffle 96. A sight line may be provided on the member 236 to provide a quick visual indication of the proper oil level in reservoir 82.

Each of the reciprocating vanes 50 and 50 is provided with a shallow oil groove 238 extending longitudinally of the end face of the vane and terminating spaced from opposite ends thereof, one of which grooves is shown in FIG. 3. As the vane 50 reciprocates upon rotation of the piston or displacer 48, its free end projects into the oil reservoir 80, and oil can thereby flow into the grooves 238 in opposite end faces of the vane to provide an oil seal between the vane and the adjacent surfaces of the blocks 30 and 34, thereby preventing any leakage across the vane.

By reference to FIGS. 2 and 5, it will be apparent that a pumping section 22 for a double stage vacuum pump may be provided by assembling the members 30, 32, 34, 36 and 38 in face-to-face relation, and securing them together by the through bolts 40 shown in FIG. 2. Some of these same basic parts may be utilized to construct a single stage vacuum pump, i.e., members 30, 32 and 38 may be assembled together in similar fashion to provide a pumping section for a single stage vacuum pump. Thus it can be seen that the same basic components can be utilized for constructing both single and multi-stage vacuum pumps, and that such parts may be stockpiled and assembled with a minimum of delay to satisfy orders as they are received.

As can be seen from FIG. 2 the oil reservoir section 24 may be easily and quickly assembled atop the pumping section 22, and the oil reservoir section 24 may be identical for double stage pumps, irrespective of whether they are to operate in series only, or whether they are provided with means for enabling both series and parallel operation. For the so-called switchable pump, i.e., one that can be operated in either series or parallel, a top cap such as shown at 26 in FIG. 2 is provided, whereas if it is desired that the pump be capable of operating in only one mode, a top cap assembly can be provided without the valve structure shown in FIG. 3 to satisfy such requirement. However, the remaining parts of the pump, namely all of the components comprising the pumping section 22 and the oil reservoir section 24 will be identical, thereby considerably simplifying the pump assembly procedures, and in addition diminishing to a great extent the number of parts necessary to be kept on hand to satisfy incoming orders.

Assuming that a double stage switchable pump is to be provided, the pumping section members 30, 32, 34, 36 and 38 of FIG. 5 are assembled together to provide the pumping section assembly 22 shown in FIG. 2, with the rotor and vane assemblies, drive shaft and exhaust stacks properly positioned as shown. The oil reservoir section 24 is then fastened atop the pumping section 22, and finally the top cap section 26 is fastened atop the reservoir section 24. The reservoir section is charged with oil until the oil reaches a level spaced slightly below the upper end of the stack 66 and 68, say about one-eighth of an inch therebelow. This oil fills all of the oil sealing grooves 42, thereby serving to provide an effective oil seal surrounding each pumping chamber 46 and 46. These oil seals eliminate the need for mechanical sealing means between the members which make up the pumping section 22 shown in FIG. 5, and thus simplify the assembly procedure and in addition are not subject to deterioration and failure as are mechanical seals. The oil in the oil reservoir 82 also fills the sealing grooves 106, 108, 110, 112, 118, 120 and 122 shown for example in FIG. 9 by virtue of the fact that the ends 114, 116, 124 and 126 of such grooves communicate with the oil reservoir 82. These grooves thereby provide an oil seal between the abutting faces of the reservoir section 24 and the pumping section 22, again eliminating the need for mechanical seals about the fluid passages therein.

The top cap section 26 is then superimposed upon the oil reservoir section 24, and the exhaust muffler 170 is threaded into the top cap exhaust port 94. The vacuum pump assembly may be either directly coupled to a suitable electric drive motor 28 as shown in FIG. 1 by connecting the shaft 56 to the output shaft of the motor 28, or the pump may be belt-driven by providing suitable pulleys and a drive belt interconnecting the pump shaft 56 and the drive shaft of the motor 28.

The two vacuum pump stages shown in FIGS. 3 and 4 are fixed to a common shaft, and thus operate in identical fashion, albeit 180 degrees out of phase, so a description of one will suffice for both. Referring to FIG. 3, with the parts positioned as shown and the rotor or displacer 48 rotating in a counterclockwise direction, the portions of the chamber 46 identified by numerals 250 and 252 are of approximately the same size. As the displacer 48 continues rotation, chamber 252 decreases in volume, compressing the gases therein and eventually opening valve 62 to exhaust the compressed gases. Meanwhile chamber 250 is increasing in volume, drawing gases from the device to be evacuated through inlet 58 into the chamber. Rotor 48 eventually reaches a position blocking outlet 60, at which point the entire pumping chamber is open to inlet 58, and the displacer begins compressing the gases therein as it continues its rotation to close inlet 58 and then to begin compression of the gases within the chamber.

With the parts completely assembled as above described, the inlet 158 in the top cap section 26 may be suitably connected to a device to be evacuated, and the motor 28 connected to a suitable electric supply to run the pump. In the case of a so-called switchable pump, the two stages of the pump shown most clearly in FIGS. 3 and 4 will be first operated in parallel until a predetermined vacuum is reached, and then the valve 142 will be shifted to switch to series operation, so that a desired high vacuum may be attained. For example, with a system at atmospheric pressure, the pump stages are operated in parallel, i.e., each stage is directly coupled to the system to be evacuated, and a partial vacuum is quickly attained. Then the pump is switched to series operation, i.e. the first stage is coupled to the system, and the second stage is coupled to the first stage exhaust, whereby a much higher vacuum may be attained. When operated in series, the pump stage shown in FIG. 3, which is the first stage, may be referred to as the roughing stage, while the second stage depicted in FIG. 4 may be referred to as the finish stage.

To operate the two stages of the pump in parallel, the spool valve 142 is positioned as shown in solid outline in FIG. 3, and the inlet 158 is connected to the device to be evacuated. With the valve in this position, the inlet passage 156 communicates with the pumping chamber 46 through the passages 84, 86 and 58, and also with the pumping chamber 46' through passages 164, 166, 168, 90, 92 and 58 (FIGS. 3, 7 and 4). Both stages of the pump are thus directly coupled to the device to achieve a predetermined vacuum therein as quickly as possible with the pump stages operating in parallel. As can be seen from FIG. 3, during this mode of operation, the pumping chamber 46 draws gases in through inlet 58 and exhausts the compressed gases through passages 60, 66 and into the oil reservoir 80, and thence through passages 88, 160, valve chamber and passage 162 into the oil reservoir 82, and thence to the outlet 94. At the same time, pumping chamber 46' draws gases in through passages 156, 164 (FIG. 3), crossover 166 (FIG. 7) and passages 168, 90, 92 and 58, and exhauststhrough passages 60, 66', 70' into the reservoir 82 and thence to the outlet 94.

When the system or device reaches a predetermined vacuum, the spool valve is shifted to its position indicated in phantom outline at 142 in FIG. 3, which switches the pump from parallel to series operation. In this position, communication between inlet 158 and passage 164 is blocked, as is communication between passages 160 and 162, while communication is established between passages 160 and 164. Thus incoming gases are introduced first through a roughing stage defined by chamber 46 in FIG. 3, and from there they pass through the exhaust and thence into finish stage 46 (FIG. 4) through passages 160, 140, 164 (FIG. 3), 166, 168 (FIG. 7), 90, 92 and 58 (FIG. 4). Exhaust from the finish stage is as before through oil reservoir 82, exhaust port 94 and muffler 170.

In FIG. 13 there is shown schematically control means for automatically switching the pump between parallel and series operation. The vacuum pump is therein identified by numeral 20 and is shown as having solenoid-operated valve 260, the valve portion of which may be similar to valve 142 (FIG. 3) and which operates in an identical fashion as previously described, except that it is solenoid-actuated rather than manually actuated. The system to be exhausted, indicated at 262, is coupled to the pump inlet 158 by asuitable conduit 264 having a Tee fitting 266. Connected to the free end of the Tee 266 is a pressure responsive switch 268, which is in turn electrically coupled to the solenoid valve 260 by suitable connectors 270. Solenoid 260 is normally in a position whereby its valve is in the position of the spool valve 142 in FIG. 3, i.e., for parallel pump operation. When the system 262 is drawn down to a predetermined point as determined by the setting of switch 268, the switch is actuated, thereby energizing the solenoid to shift its valve to the position wherein the pump is operated in series. If pressure in the system again rises past the setting of switch 268, the solenoid will be deenergized, shifting the valve back to its parallel operating position.

In a double stage pump as depicted in the drawings, both gas ballast and oil injection are provided in the second or finish pump stage. Gas ballast is accomplished through the passage 174 (FIGS. 4 and 10) and opening of the valve 184 serves to connect such passage to atmosphere so that as the piston 48' rotates counterclockwise as shown in FIG. 4, it passes passage 174 shortly after start of its compression cycle. Air is therefore introduced into the chamber 46' during that portion of the piston stroke when the chamber pressure is below atmospheric. As the piston 48' continues its rotation, passage 174 is obturated by the piston face, closing off the air ballast during the remainder of the piston stroke.

Oil injection into the chamber 46' is governed by the valve 200 (FIGS. 6 and 12) and obturation of the port 194 by the piston is not relied upon to shut off the oil injection. Referring to FIG. 4, just after the piston passes inlet 58 the pressure in the chamber 46' is at minimum and the pressure of the oil in passage 190, 198, which is at atmosphere plus the head of oil in the oil reservoir 82 and groove 42, overcomes the pressure of spring 202 against valve 200, opening the valve to admit oil to the chamber 46. As the piston continues its rotation, pressure in the chamber increases due to compression of the gas therein, until the gas pressure plus the spring pressure overcomes the pressure of the oil in passage 190, 198, closing the valve. The pressure of spring 202 determines the length of time the valve 200 is open, and hence by variation of the spring pressure, the amount of oil injected may be varied.

What is claimed is:

1. A multi-stage rotary vacuum pump comprising, in combination: a lower pumping section; an intermediate oil reservoir section; and a manifold cover section; said pumping section including a plurality of block-like members each having spaced parallel end faces secured together in end-to-end face-abutting relation, certain of said members defining cylindrical pumping chambers and other of said members defining end closures for said chambers, a common shaft extending through said chambers with an eccentric displacer thereon for each chamber having a vane projecting therefrom dividing its respective chamber in two, an inlet and an outlet in each chamber spaced on opposite sides of said vane closely adjacent thereto; said oil reservoir section comprising a unitary housing secured atop said block-like members and having a separate oil reservoir for each pump chamber communicating with a respective chamber outlet and an opening through the reservoir top wall; and said manifold cover section comprising a single piece'cover mounted atop said oil reservoir section and having fluid conducting passages communicating with each reservoir opening and a common fluid outlet in the top of the cover communicating with each said passage.

2. A rotary vacuum pump as defined in claim 1 characterized in that said oil reservoir section and said cover section each define fluid passage means establishing communication between the device to be evacuated and each of the pumping chambers.

3. A rotary vacuum pump as defined in claim 2 characterized in that said reservoir section includes a separate inlet passage communicating with each of said chamber inlets and said cover section includes a single inlet port adapted to be coupled to the device to be evacuated and a plurality of inlet passages communicating with said reservoir passages, and valve means selectively operable to open and close predetermined of said passages for connecting said pump chambers to said device in series or in parallel. 

1. A multi-stage rotary vacuum pump comprising, in combination: a lower pumping section; an intermediate oil reservoir section; and a manifold cover section; said pumping section including a plurality of block-like members each having spaced parallel end faces secured together in end-to-end face-abutting relation, certain of said members defining cylindrical pumping chambers and other of said members defining end closures for said chambers, a common shaft extending through said chambers with an eccentric displacer thereon for each chamber having a vane projecting therefrom dividing its respective chamber in two, an inlet and an outlet in each chamber spaced on opposite sides of said vane closely adjacent thereto; said oil reservoir section comprising a unitary housing secured atop said block-like members and having a separate oil reservoir for each pump chamber communicating with a respective chamber outlet and an opening through the reservoir top wall; and said manifold cover section comprising a single piece cover mounted atop said oil reservoir section and having fluid conducting passages communicating with each reservoir opening and a common fluid outlet in the top of the cover communicating with each said passage.
 2. A rotary vacuum pump as defined in claim 1 characterized in that said oil reservoir section and said cover section each define fluid passage means establishing communication between the device to be evacuated and each of the pumping chambers.
 3. A rotary vacuum pump as defined in claim 2 characterized in that said reservoir section includes a separate inlet passage communicating with each of said chamber inlets and said cover section includes a single inlet port adapted to be coupled to the device to be evacuated and a plurality of inlet passages communicating with said reservoir passages, and valve means selectively operable to open and close predetermined of said passages for connecting said pump chambers to said device in series or in parallel. 